[wasm] WIP fix arm64 frame alignment.

src/compiler/arm64/instruction-selector-arm64.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 1613 matching lines @@
 void InstructionSelector::VisitFloat64RoundTiesEven(Node* node) {
   VisitRR(this, kArm64Float64RoundTiesEven, node);
 }
 
 
 void InstructionSelector::EmitPrepareArguments(
     ZoneVector<PushParameter>* arguments, const CallDescriptor* descriptor,
     Node* node) {
   Arm64OperandGenerator g(this);
 
+  bool from_native_stack = linkage()->GetIncomingDescriptor()->UseNativeStack();
   bool to_native_stack = descriptor->UseNativeStack();
 
+  bool always_claim = to_native_stack != from_native_stack;
+
   int claim_count = static_cast<int>(arguments->size());
   int slot = claim_count - 1;
-  if (to_native_stack) {
-    // Native stack must always be aligned to 16 (2 words).
-    claim_count = RoundUp(claim_count, 2);
-  }
-  // TODO(titzer): claim and poke probably take small immediates.
   // Bump the stack pointer(s).
-  if (claim_count > 0 || to_native_stack) {
+  if (claim_count > 0 || always_claim) {
+    // TODO(titzer): claim and poke probably take small immediates.
     // TODO(titzer): it would be better to bump the csp here only
     //                and emit paired stores with increment for non c frames.
     ArchOpcode claim = to_native_stack ? kArm64ClaimCSP : kArm64ClaimJSSP;
     Emit(claim, g.NoOutput(), g.TempImmediate(claim_count));

[ahaas, 2016/03/29 08:33:58]

Could you add a comment here why "claim(0)" isn't a nop?

[titzer, 2016/03/29 09:10:53]

Done.

   }
 
   // Poke the arguments into the stack.
   ArchOpcode poke = to_native_stack ? kArm64PokeCSP : kArm64PokeJSSP;
   while (slot >= 0) {
     Emit(poke, g.NoOutput(), g.UseRegister((*arguments)[slot].node()),
          g.TempImmediate(slot));
     slot--;
     // TODO(ahaas): Poke arguments in pairs if two subsequent arguments have the
     //              same type.
@@ skipping 604 matching lines @@
          MachineOperatorBuilder::kWord32ShiftIsSafe |
          MachineOperatorBuilder::kInt32DivIsSafe |
          MachineOperatorBuilder::kUint32DivIsSafe |
          MachineOperatorBuilder::kWord32ReverseBits |
          MachineOperatorBuilder::kWord64ReverseBits;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8